Autotetraploid Induction of Cercis canadensis by Oryzalin and Colchicine Agar Drop Technique

Eastern redbud, Cercis canadensis L., is a deciduous flowering tree species with great ornamental value. In 2019, redbuds had an estimated economic value of $28.4 million in the United States, with C. canadensis comprising the majority of this market. Ploidy manipulation is a powerful tool in ornamental plant breeding for developing cultivars with novel traits; however, no studies of polyploidy induction in C. canadensis have been reported to date. To develop a genome doubling protocol, two mitotic inhibitors—oryzalin and colchicine—were applied to C. canadensis seedlings using the agar drop method, with varying concentrations and treatment durations. The ploidy levels of surviving plants were evaluated using flow cytometry. In the first experiment, oryzalin treatments yielded a tetraploid conversion rate three-times higher than that of colchicine treatments, despite colchicine being applied at concentrations 100-times greater. In the second experiment, increasing concentrations of oryzalin (150, 300, and 450 μM) did not significantly affect polyploid induction, and no statistically significant differences were observed in either survival or tetraploid conversion ratios. In the third experiment, extending treatment duration led to increased frequencies of tetraploid and mixoploid seedlings, although the increase in tetraploid conversion ratio was not statistically significant. Among all treatments, the 150 μM oryzalin treatment applied for 9 days yielded the optimal results: a 55.15% survival rate and 15.38% of surviving seedlings confirmed as tetraploid. This study presents the first established protocol for polyploidy induction in C. canadensis and offers a valuable tool for breeding novel cultivars of eastern redbuds and redbud species.